The principal objective of this research is to develop bioerodible drug delivery devices that will release a therapeutic agent in response to an external signal. The delivery device is activated by the interaction of a specific external molecule with an enzyme-antigen complex. This interaction leads to a pH change, which in turn initiates or modifies the erosion of a hydrophobic polymer containing the therapeutic agent incorporated therein. Development of two specific systems is proposed: Devices that release a narcotic antagonist in response to external opiates, and a contraceptive device that release an appropriate agent in response to human chorionic gonadotropins. However, these two systems are viewed principally as models, and development of other medically significant devices would be feasible. High on the list of priorities would be prophylactic devices to guard against parasitic invasion.